Triggering initiation of a sheetfeed operation from backward movement of the platen of the printer with which the sheetfeed is mounted is a standard alternative. Illustrative of such a sheetfeed is is IBM Technical Disclosure Bulletin article entitled "Bidirectional Clutch Spring," Vol. 30, No. 4, Sept. 1987 at pp. 1578-1580. A backward platen movement of a predetermined amount physically moves a latch to free the sheetfeed for feeding one sheet of paper in response to forward platen movement. Such a system avoids electrical connection to the sheetfeed, which may be entirely mechanical.
This invention employs a paper-presence sensor. Such sensors are widely known, but not for purposes of control of a sheetfeed for back up to erase. U.S. Pat. No. 4,655,626 to Okazaki is of general interest with respect to this invention in that it shows paper-presence sensing in a sheetfeed.